RESEARCH ARTICLE Open Access

Short-term effects of a nicotine-freee-cigarette compared to a traditionalcigarette in smokers and non-smokersMarco Ferrari1, Alessandro Zanasi2, Elena Nardi4, Antonio Maria Morselli Labate4, Piero Ceriana3,Antonella Balestrino3, Lara Pisani1, Nadia Corcione1 and Stefano Nava1,2*

Abstract

Background: A few studies have assessed the short-term effects of low-dose nicotine e-cigarettes, while data aboutnicotine-free e-cigarettes (NF e-cigarettes) are scanty. Concerns have been expressed about the use of NF e-cigarettes,because of the high concentrations of propylene glycol and other compounds in the e-cigarette vapor.

Methods: This laboratory-based study was aimed to compare the effects of ad libitum use of a NF e-cigarette or and atraditional cigarette for 5 min in healthy adult smokers (n = 10) and non-smokers (n = 10).The main outcome measures were pulmonary function tests, fraction of exhaled nitric oxide (FeNO) and fractionalconcentration of carbon monoxide (FeCO) in exhaled breath.

Results: The traditional cigarette induced statistically significant increases in FeCO in both smokers and non-smokers,while no significant changes were observed in FeNO. In non-smokers, the traditional cigarette induced a significantdecrease from baseline in FEF75 (81 % ± 35 % vs 70.2 % ± 28.2 %, P = 0.013), while in smokers significant decreases wereobserved in FEF25 (101.3 % ± 16.4 % vs 93.5 % ± 31.7 %, P = 0.037), FEV1 (102.2 % ± 9.5 % vs 98.3 % ± 10 %, P = 0.037) andPEF (109.5 % ± 14.6 % vs 99.2 % ± 17.5 %, P = 0.009). In contrast, the only statistically significant effects induced by the NFe-cigarette in smokers were reductions in FEV1 (102.2 % ± 9.5 % vs 99.5 ± 7.6 %, P = 0.041) and FEF25 (103.4 % ± 16.4 %vs 94.2 % ± 16.2 %, P = 0.014).

Discussion: The present study demonstrated that the specific brand of NF e-cigarette utilized did not induceany majoracute effects. In contrast, several studies have shown that both traditional cigarettes and nicotine-containing e-cigarettes have acute effects on lung function. Our study expands on previous observations onthe effects of NF e-cigarettes, but also for the first time describes the changes induced by smoking onetraditional cigarette in a group of never smokers.

Conclusions: The short-term use of the specific brand of NF e-cigarette assessed in this study had no immediateadverse effects on non-smokers and only small effects on FEV1 and FEF25 in smokers. The long-term health effectsof NF e-cigarette use are unknown but worthy of further investigations.

Trial registration: Clinicaltrials.gov: NCT02102191

Keywords: Electronic cigarettes, Pulmonary function tests, Smoking, Concentration of carbon monoxide inexhaled breath

* Correspondence: stefanava@gmail.com1Department of Specialistic, Diagnostic and Experimental Medicine,Respiratory and Critical Care Unit, Alma Mater Studiorum, Sant’OrsolaMalpighi Hospital, University of Bologna, Bologna, Italy2Respiratory and Critical Care Unit, Sant’Orsola Malpighi Hospital, ViaMassarenti 9, 40138 Bologna, ItalyFull list of author information is available at the end of the article

© 2015 Ferrari et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Ferrari et al. BMC Pulmonary Medicine (2015) 15:120 DOI 10.1186/s12890-015-0106-z

BackgroundElectronic cigarettes (e-cigarettes) have been proposedas a novel method for quitting smoking. The producersof e-cigarettes claim that one of the benefits of these cig-arettes is that a smoker may gradually decrease the nico-tine content over time, until a state of “nicotine-free”smoking is reached. This state can be reached withoutthe smoker having to renounce “habit-automatisms” andhandling, which are major obstacles to quitting smoking.However, the recent position statement of the Forum

of International Respiratory Societies [1] on the use ofe-cigarettes and their potential hazards concluded thatthese devices should be restricted or banned until moreinformation about their safety is available. The majorconcerns include the nicotine content and the potentialharm due to the high concentrations of propylene gly-col, which is irritant when inhaled, chemicals, such asquinoline, benzoic acid and diethylcarbonate, and othercompounds found in the e-cigarette vapor.To our knowledge there are no data on the health effects

of acute use of nicotine-free e-cigarettes (NF e-cigarettes);we, therefore, designed a study to compare the changes inpulmonary function tests (PFT) and fractions of exhalednitric oxide (FeNO) and carbon monoxide (FeCO) as a re-sult of 5 min of ad libitum smoking of a NF e-cigarette ora traditional cigarette, in smokers and non-smokers.

MethodsSubjectsTwenty normal subjects, recruited among pulmonary fel-lows or attending physicians were studied: 10 weresmokers (minimum of 5 pack-years) and 10 were non-smokers. Exclusion criteria were current use of any medi-cation, the presence of any acute or chronic lung disease,neuromuscular diseases, cancer, chronic heart failure,metabolic or auto-immune diseases and acute illness dur-ing the preceding 4 weeks. Each subject was asked to signwritten informed consent to the protocol approved by theSalvatore Maugeri Ethical Committee. The protocol wasregistered at www.clinicaltrials.gov with the numberNCT02102191 on March 27, 2014.

ProtocolBoth smokers and non-smokers were randomized tosmoke both the NF e-cigarette and a commercial “popularbrand” standard cigarette ad libitum for 5 min in two dif-ferent sessions according to a cross-over design (5 patientswithin each group smoked first the NF e-cigarette andthen the commercial cigarette and 5 subjects smoked firstthe commercial and then the NF e-cigarette). All subjectswere asked to use a similar pattern and frequency ofsmoke aspiration, although it cannot be assured that theydid so. The subjects were also asked to refrain from

smoking in the 6 h preceding the test session and not toeat or drink for at least 4 h prior to the experimentalprocedure.The first smoking session started 5 min after the base-

line measurement of FeCO, FeNO and PFT. The secondsmoking session started after a wash-out of 24 h afterthe end of the first session. This wash-out period was toensure that there was no carry-over effect. The measure-ments of FeNO, FeCO and PFTs were repeated immedi-ately after each smoking session.The NF e-cigarette used in this study, ELIPS C Series

(Ovale Europe S.r.l., Desenzano del Garda, Brescia, Italy),was a brand commercially available in Italy. It was formedof a steel shell with a microprocessor powered by a bat-tery, a filter and a removable cartridge. Among the six dif-ferent types of cartridge available, we chose “Natur Smokearoma Nocciola Antistress 0 mg/mL nicotina” (Angelica,Bologna, Italy), i.e., a nicotine-free liquid with a hazelnutflavorThe liquid of the cartridge is registered by the ItalianRegulatory Agency and had the following composition:glycerin >50 %, isotonic solution 5–10 %, magnesiumchloride 1–5 %, natural flavor 0.1–1 %, and vitamin B120.1–1 %. The specific kind of NF e-cigarette chosen in thecurrent study followed an unbiased internet search forproducts available and produced in Italy (e.g.Dea, Flatech,Flavour Roma). Use of the Angelica liquid was finally de-cided mainly due to logistic convenience since it was pro-duced in the same city (Bologna) of investigation.The commercial standard cigarette, Marlboro® Red Label

Box (Philip Morris USA Inc., Miami, FL, USA), containednicotine 0.8 mg, carbon oxide (CO) 10 mg and tar 10 mg.According to the manufacturer [2], the components notexceeding 0.1 % of the weight of the tobacco were aceticacid 0.01, acetophenone 0.0001, ammonium hydroxide0.3, amyl butyrate 0.0001, benzaldehyde 0.005, benzoin0.005, benzyl alcohol 0.1, cellulose 9.3, calcium carbonate4.6, monopotassium phosphate 1.4, potassium citrate 0.3,guar gum 0.1, and hercon70 0.1.

MeasurementsThe exhaled nitric oxide (FeNO) and fractional concen-tration of carbon monoxide in exhaled breath (FeCO)were measured using chemiluminescense analyzers(NIOX MINO, Aerocrine AB, Solna, Sweden and MicroSmokerlyzer, Bedfont Scientific Ltd., Rochester, Kent,Great Britain, respectively) with a computerized pro-gram. The FeNO analyzer was calibrated with certifiedNO mixtures (100 ppb) in nitrogen.PFT were performed with a spirometer (Chestgraph

HI-105 - CHEST M.I. Inc, Tokyo, Japan). The followingparameters were recorded in the sitting position: forcedvital capacity (FVC), forced expiratory volume in 1 s(FEV1), forced expiratory flow (FEF) 25 %, 50 % and75 % and peak expiratory flow (PEF). Spirometry was

Ferrari et al. BMC Pulmonary Medicine (2015) 15:120 Page 2 of 9

performed following the recommendations of theAmerican Thoracic Society/European Respiratory Soci-ety (ATS/ERS) guidelines [3].For the FeNO recording, the subjects were studied in

the sitting position wearing a nose-clip and were askedto inhale as deeply as they could, to total lung capacity,while breathing through a mouthpiece and then to ex-hale at a flow rate of about 50 mL/s, maintaining a con-stant mouth pressure of 4 to 5 cm H2O for 10 s, aidedby visual feedback on the screen of the instrument.Each of the three different measurements (FeNO, FeCO

and PFT) were separated by intervals of about 45 s.

Statistical analysisData are expressed as mean ± SD or as frequencies. AKolmogorov-Smirnov non-parametric test was applied totest the normality of the distributions. Two-way ANOVAwas applied to the differences observed between basalvalues and those after smoking a traditional cigarette oran e-cigarette, considering smoking habit and the cross-over design as factors. The effects estimated by ANOVAare reported together with their 95 % confidence intervals(95 % CI). A two-tailed P value less than 0.05 is consideredstatistically significant. All analyses were performed usingSPSS for Windows (ver. 21, IBM Corporation, Armonk,NY, USA).

Sample sizeProkhorov et al. found a decrease of 2.14 % in the pre-dicted value of FEV1 in 18 volunteer, regular smokers aftersmoking one traditional cigarette [4]. Since the standarddeviation of the within-subject difference was not re-ported, we have estimated this value as 3.26 % (one thirdof the value reported as the overall standard deviation inthe study by Prokhorov et al.; i.e., 9.78 %) [4]. By compar-ing these values versus no effect of the e-cigarette, we hadto study 20 subjects in order to be able to reject the nullhypothesis with a probability (power) of 0.80 and atwo-sided type I error probability of 0.05. We, there-fore, set the sample size as 20 subjects (10 smokers and10 non-smokers), hypothesizing similar effects ofsmoking one traditional cigarette between smokers and

non-smokers. The sample size was estimated by meansof “PS Power and Sample Size Calculations” software(Version 3.0.43; Department of Statistics of the Vander-bilt University, Nashville, TN, USA; http://biostat.mc.-vanderbilt.edu/twiki/bin/view/Main/PowerSampleSize)according to Dupont and Plummer [5].

ResultsThe subjects’ characteristics are reported in Table 1.All the subjects completed the study protocol. A few

non-smokers reported mild adverse events such as drycough (n = 3) and throat irritation (n = 2) when smokingtraditional cigarettes.

FeCO and FeNOThe FeCO values in the smokers and non-smokers areshown in Figure 1. As expected, baseline FeCO valueswere significantly higher in smokers than in non-smokers (P < 0.001,two-way ANOVA). The signifycance values, using the two-way ANOVA analysis, of the

changes of FeCO values versus the baseline ones observedin smokers and non-smokers after smoking each type ofcigarette, as well as the comparison between the traditionaland e-cigarette, are also shown in Fig. 1 while the estimatedeffects of the two different types of cigarette in the overallpopulation and the comparison of these effects betweensmokers and non-smokers, using the two-way ANOVAanalysis, are presented in Table 2. In the 20 subjects studiedthe traditional cigarette significantly increased FeCOvalues (P < 0.001); this effect was significant in bothgroups of subjects (smokers P < 0.001; non-smokersP = 0.043). In contrast, the e-cigarette did not haveany significant effects on FeCO (overall populationP = 0.486; smokers P = 0.226; non-smokers P = 0.804).The increase of FeCO values observed after smokingthe traditional cigarette was significantly differentfrom the effect of the e-cigarette (overall populationP < 0.001; smokers P < 0.001; non-smokers P = 0.048).As far as the comparison between smokers and non-smokers is concerned, no significant differences werefound (traditional cigarette P = 0.127; e-cigarette P = 0.301).Likewise, the difference observed between the two types of

Table 1 Subjects’ characteristics

Overall Smokers Non-smokers P value

Gender (M/F) 11/9 4/6 7/3 0.370a

Age (mean ± SD, years) 39.3 ± 12.6 42.3 ± 12.8 36.2 ± 12.3 0.291b

Weight (mean ± SD, kg) 67.9 ± 10.4 63.5 ± 10.1 72.3 ± 9.2 0.056b

Height (mean ± SD, cm) 169. ± 10.0 163 ± 7.4 176 ± 8.3 0.002b

BMI (mean ± SD, kg/m2) 23.5 ± 2.5 23.7 ± 3.1 23.3 ± 1.9 0.704b

Smoke history (pack-years) - mean ± SD (range) - 19.4 ± 10.8 (5–35) - -aFisher’s exact testbt-test for equality of means

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cigarette was not significant between smokers and non-smokers (P = 0.067).Baseline values of FeNO were not significantly different

between smokers and non-smokers (P = 0.245, two-wayANOVA). No significant changes of FeNO were observedin the two groups of subjects after smoking either a trad-itional or e-cigarette (Fig. 2, two-way ANOVA) and no sig-nificant changes were found in the overall group ofsubjects studied (Table 2).

Pulmonary function testsAll baseline pulmonary function tests (FEV1, FVC,FEV1/FVC, and PEF) were similar between smokers andnon-smokers (P ≥ 0.157,Two-way ANOVA).Smoking a traditional cigarette significantly de-

creased the FEV1/FVC in non-smokers (P = 0.047 twoway ANOVA; Fig. 3). In addition, both types of ciga-rettes significantly decreased FEV1 values in smokers(traditional P = 0.037; electronic P = 0.041, two-wayANOVA) while the decreases in non-smokers were notsignificant; thus FEV1 decreased significantly in theoverall population (P = 0.013, Two-way ANOVA) aftersmoking a traditional cigarette while the effect of thee-cigarette did not reach a statistically significant level(P = 0.070, Two-way ANOVA). Finally, the traditionalcigarette significantly decreased PEF values in the over-all population (P = 0.017, Two-way ANOVA) due to ef-fect in the smokers (P = 0.009,Two-way ANOVA). Thechanges in FEV1, FVC, FEV1/FVC, and PEF betweenthe two types of cigarettes were not significantly differ-ent in either smokers or non-smokers (Fig. 3) or, in-deed in the overall population (Table 2).As far as FEF values are concerned, the traditional

cigarette significantly decreased FEF25, FEF50 and FEF75in the overall population (P = 0.030, P = 0.033, and P =

0.040, respectively, two-way ANOVA; Table 2), particu-larly due to the significant reductions of FEF25 in smokers(P = 0.037) and FEF75 in non-smokers (P = 0.013) whilethe reduction of FEF50 did not reach the significant levelsin either smokers (P = 0.213) or non-smokers (P = 0.063)(Fig. 4). The only significant effect of the e-cigarette was areduction of FEF25 in smokers (P = 0.014, two-wayANOVA). Comparing the effects of traditional and e-cigarette smoking, only a significantly greater reduction ofFEF50 was found after traditional cigarette smoking innon-smokers (P = 0.036, two-way ANOVA).As far as concerns the comparison between smokers

and non-smokers, higher values of FEF75 were foundafter smoking an e-cigarette than after smoking a trad-itional cigarette, whereas the inverse was the case insmokers (P = 0.037, two-way ANOVA) (Table 2,Fig. 4c).

DiscussionWe found that the specific brand of NF e-cigarettes usedin this study was not associated with major acute physio-logical changes, causing only small, albeit statisticallysignificant decreases in FEF25 and FEV1 in the group ofsmokers. In contrast, smoking a traditional cigarette in-duced immediate bronchoconstriction in non-smokers.Tobacco cigarettes are one of the most important risk

factors for disease worldwide and the primary goal of to-bacco control is to reduce the mortality and morbidityassociated with its use.E-cigarettes have gained popularity in the last few

years, mainly because of the advertisements of their pro-ducers, who claim that smoking tar-free cigarettes is as-sociated with reduced risk for the health.A recent systematic review assessing the efficacy of e-

cigarettes included six experimental studies and six cohortstudies. The authors concluded that the use of e-cigarettes

Fig. 1 Changes in fractional concentration of carbon monoxide in exhaled breath (FeCO) in smokers and non smokers

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can reduce the number of cigarettes smoked and with-drawal symptoms, but that it was associated with some ad-verse events, such as mouth and throat irritation, nausea,headache and dry cough [6].E-cigarettes have been shown to induce immediate ad-

verse physiological effects after short-term use, similar tothose observed with tobacco smoking [7]. The statement

of the Forum of International Respiratory Societies [1] onthe use of e-cigarettes and their potential hazards con-cluded that, considering the above-mentioned facts, theuse of these devices should be restricted until more infor-mation on their safety becomes available.More recently, NF e-cigarettes have been released

on the market with the aim of minimizing the

Table 2 Effects of the two different types of cigarette

Overall population Smokers vs. non smokers

Effect 95 % CI P Effect 95 % CI P

FeCO (ppm)

Traditional 4.3 (2.3 to 6.2) <0.001 2.9 (−0.9 to 6.7) 0.127

Electronic −0.2 (−0.8 to 0.4) 0.486 −0.6 (−1.8 to 0.6) 0.301

P value <0.001 0.067

FeNO (ppb)

Traditional −0.6 (−1.6 to 0.4) 0.219 1.4 (−0.6 to 3.4) 0.155

Electronic −0.2 (−0.8 to 0.4) 0.512 0.8 (−0.5 to 2.1) 0.198

P value 0.372 0.501

FEV1 (%)

Traditional −3.4 (−5.9 to −0.8) 0.013 −1.0 (−6.1 to 4.1) 0.691

Electronic −1.7 (−4.8 to 2.9) 0.070 −2.1 (−5.7 to 1.6) 0.250

P value 0.098 0.575

FVC (%)

Traditional −1.6 (−5.7 to 2.6) 0.437 −3.9 (−12.2 to 4.4) 0.331

Electronic −1.0 (−4.8 to 2.9) 0.602 −2.2 (−9.8 to 5.4) 0.543

P value 0.584 0.448

FEV1/FVC

Traditional −1.9 (−3.9 to 0.1) 0.065 2.0 (−2.0 to 6.1) 0.304

Electronic −0.9 (−2.5 to 0.6) 0.226 −0.1 (−9.8 to 3.0) 0.926

P value 0.182 0.132

PEF (%)

Traditional −6.5 (−11.7 to −1.3) 0.017 −7.5 (−17.8 to 2.9) 0.148

Electronic −3.8 (−9.2 to 1.6) 0.155 −6.0 (−16.8 to 4.8) 0.254

P value 0.145 0.692

FEF25 (%)

Traditional −5.8 (−10.9 to −0.6) 0.030 .4.1 (−14.1 to 6.2) 0.412

Electronic −3.7 (−7.6 to 0.3) 0.066 −7.1 (−15.0 to 0.7) 0.073

P value 0.252 0.414

FEF50 (%)

Traditional −5.0 (−9.5 to −0.4) 0.033 2.1 (−6.9 to 11.1) 0.629

Electronic −2.9 (−6.8 to 1.1) 0.143 −2.9 (−10.8 to 5.0) 0.447

P value 0.161 0.096

FEF75 (%)

Traditional −6.1 (−11.9 to −0.3) 0.040 9.3 (−2.3 to 20.9) 0.107

Electronic −4.8 (−11.2 to 1.6) 0.132 3.6 (−16.4 to 9.3) 0.562

P value 0.657 0.037

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adverse events linked with the use of nicotine-delivering e-cigarettes.One of the concerns of using NF e-cigarettes is that

the devices contain high concentrations of glycol, whichis a known irritant when inhaled. Other potentially dan-gerous ingredients that may be found in NF e-cigarettes

are solvents, genotoxins and various other chemicals andanimal carcinogens (e.g., benzoic acid, quinoline).The act of ‘smoking’ an e-cigarette is called ‘vaping’

and it mimics smoking so, in addition to deliveringnicotine, it can address both pharmacological and be-havioral components of cigarette addiction. Indeed, the

Fig. 2 Changes in fraction of exhaled nitric oxide (FeNO) in smokers and non smokers

Fig. 3 Changes in pulmonary function tests in smokers and non smokers

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notable reduction in craving achieved by NF e-cigarettesdemonstrates the ability of physical stimuli to suppresscravings independently of the administration of nicotine[8–13].In a randomized, controlled trial of smoking cessation

aided by nicotine e-cigarettes, NF e-cigarettes or nico-tine patches performed in 657 people, Bullen et al. [13]found a rather disappointing percentage of abstinence at6 months and the modest overall effect of the threemethods (nicotine e-cigarettes, NF e-cigarettes, nicotinepatches) did not allow a demonstration of the superiorityof nicotine e-cigarettes over NF e-cigarettes.The present study demonstrated that the specific

brand of NF e-cigarette utilized did not induce anymajor acute effects. In contrast, several studies haveshown that both traditional cigarettes and nicotine-containing e-cigarettes have acute effects on lungfunction: Vardavas et al. [7] showed that e-cigarettescontaining a dose of 11 mg of nicotine significantlyincreased the impedance and resistance after 5 min ofsmoking, while Flouris et al. [12] demonstrated a signifi-cant immediate decrease in lung function only whensmoking traditional cigarettes and not with e-cigarettes.

Similar data were also reported by Unverdorben et al.[14], who showed a significantly greater decrease inspecific airway conductance and FEF25 after smoking aconventional cigarette than after a low nicotine (5 mg)e-cigarette.Our study expands on previous observations on the

effects of NF e-cigarettes, but also for the first time de-scribes the changes induced by smoking one traditionalcigarette in a group of never smokers. Interestingly inthese subjects the decreases in PFT values were muchmore pronounced (although not-significantly) than inthe smokers, possibly because the airways of the formerwere more ‘naïve’ to noxious stimuli, which may haveinduced greater narrowing of the lumen of the periph-eral airways, due to localized edema or smooth musclecontraction. The change in pulmonary function of thesmokers was less pronounced than that reported insome previous studies and did not achieve statistical sig-nificance, despite the rate of change being quite similarto the above mentioned investigations. This may be dueto the less sophisticated method of assessing airway nar-rowing in our study than in the study by Vardavas et al.(PTF vs impulse oscillometry, respectively) [7] or the

Fig. 4 Changes in ”small airways flows” in smokers and non smokers

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longer and more intense habit of smoking of our groupof subjects, which could have minimized the response.The specific brand of NF e-cigarettes used in the present

study did not induce any significant changes in smokersapart from decreases in FEV1 and FEF25. This latter find-ing is not easy to explain, and there are no investigationsso far that have assessed the potential role of componentsof NF e-cigarettes on airway reactivity. Although bothgroups of subjects inhaled effectively - as illustrated by thesignificant increase in FeCO - only the group of activesmokers reached levels of CO suggestive of deep inhal-ation (about 20 ppm), while the non-smokers had lowervalues (about 5 ppm). The higher levels of FeCO observedin smokers than in non-smokers may be explained by theprevious CO exposure from tobacco smoking in theformer. Indeed, according to the study protocol, smokersshould have refrained from smoking in the 6 h precedingthe experiments while the half-life of expired CO is about4 h, depending on exercise.As expected, the FeNO level was reduced in the

smokers, but no significant changes were observed ineither group after cigarettes smoking. This is in contrastto what was observed in several studies [15–18], but notwith the data of Chambers et al. [19] who found an in-crease in the level of exhaled NO minutes after smoking atraditional cigarette. Balint et al. [20] also found no signifi-cant change in the concentration of exhaled NO aftersmoking two cigarettes, but the concentrations of NO me-tabolites (NO2

− +NO3−) were significantly increased. These

findings suggest that NO might be trapped at the epithe-lial surface of airways in the formation of bioequivalentoxides of nitrogen such as peroxynitrite and S-nitrosothio.The present study has some limitations that need to

be discussed. First, the technique used to detect airwaynarrowing may not be as sensitive as the impulse oscil-latory technique and it has been shown that changes inflow resistance usually precede variations in PFT. In-deed we assessed only crude spirometry, while DLCOand lung volumes and perhaps measurements of airwayreactivity and particulate/vapor burden, may have givenmore insights into the problem. The ad libitum smok-ing of the cigarette may also be criticized because ofthe lack of standardization between subjects and be-cause it is likely that a current smoker would smokemore than a non–smoker. The sample size (20 subjects)may be considered quite small, although it was based on asophisticated calculation involving previously reporteddata (4,5), so we are confident that the data collectedmay be representative enough of the changes inducedby smoking either NF e-cigarettes or traditional ones.

ConclusionsIn conclusion, smoking the NF e-cigarette studied in thepresent investigation had no immediate adverse effects

after short-term use in non-smokers and a small effecton FEV1 and FEF25 in smokers. In contrast, acute trad-itional cigarette smoking was associated with more detri-mental effects on PFT in non-smokers than in smokers,although differences were not statistically significant.The long-term health effects of NF e-cigarette use areunknown but worthy of further investigation.

Abbreviations(NF e-cigarettes): Nicotine-free e-cigarettes; (FeNO): Fractional exhaled nitricoxide; (FeCO): Fractional concentration of carbon monoxide;(PTF): Pulmonary function tests.

Competing interestsThe authors declare that they have no competing interests.

Authors’ contributionsMF = performed experiments, analyzed data and drafted the manuscript. Hehave given final approval of the version to be published. AZ = Gavesubstantial contributions to the conception and design of the study, dataacquisition and performed experiments. He have given final approval of theversion to be published. EN = data analysis and statistical analysis. Drafting ofthe manuscript. She have given final approval of the version to be published.AMML = statistical and data analysis. Gave substantial contributions to theconception and design of the study. He have given final approval of theversion to be published. PC = data analysis and drafting of the manuscript.He have given final approval of the version to be published. AB = dataanalysis and drafting of the manuscript. She have given final approval of theversion to be published. LP = performed experiments and collected data.Contributed to manuscript drafting. She have given final approval of theversion to be published. NC = performed experiments and collected data.Contributing to the manuscript drafting. She have given final approval of theversion to be published. SN = Principal Investigator. Designed the study,performed experiments, and wrote the manuscript. All authors read andapproved the final manuscript.

Author details1Department of Specialistic, Diagnostic and Experimental Medicine,Respiratory and Critical Care Unit, Alma Mater Studiorum, Sant’OrsolaMalpighi Hospital, University of Bologna, Bologna, Italy. 2Respiratory andCritical Care Unit, Sant’Orsola Malpighi Hospital, Via Massarenti 9, 40138Bologna, Italy. 3Respiratory Unit, Fondazione S.Maugeri, IRCCS, IstitutoScientifico di Pavia, Pavia, Italy. 4Laboratory of Biostatistics, Department ofMedical and Surgical Sciences (DIMEC), Alma Mater Studiorum, University ofBologna, Bologna, Italy.

Received: 19 January 2015 Accepted: 21 September 2015

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